Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so safety is fully covered. The description still earns credit by adding account-scoping, the liveness qualifier ('live' instances), the field set returned, and the session-selection fact — context not derivable from the annotations. It does not describe pagination or what happens when no engine is connected, which is why it is not a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

One sentence, front-loaded with the verb and scope, with the returned fields folded into a tight parenthetical. Nothing is redundant, though the dense comma-separated parenthetical plus the trailing 'which one this session has selected' clause make it slightly harder to parse than it needs to be.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a zero-parameter, read-only, closed-world list tool with full annotation coverage, the description supplies what the schema cannot: what an 'instance' consists of and what the session-selected flag means. With no output schema present, a brief note on the empty-account case or ordering would have closed the remaining gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool takes zero parameters, so the baseline is 4 and there is no parameter semantics for the description to compensate for. The field list in parentheses is return-value information rather than argument guidance, so it does not shift this dimension up or down.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource — 'List the live game-engine instances connected for your account' — and enumerates the fields returned (engine, project, machine, connected/last-active), so the agent knows exactly what it gets. It stops short of naming the siblings enroll_engine_plugin or select_engine_instance, so differentiation comes mostly from the tool name rather than the prose.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied: the mention of 'which one this session has selected' hints that this is the discovery step before select_engine_instance, but the description never says when to call it, when not to, or which sibling to use to change the selection. A single routing clause pointing at select_engine_instance would have moved this to a 4 or 5.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.